It is common in transport refrigeration systems, such as those for trucks, trailers and containers, to drive a refrigerant compressor with an internal combustion engine when the system is away from a terminal, and to drive the compressor via an electric motor when a source of electrical potential is available. As disclosed in U.S. Pat. No. 3,720,842, which is assigned to the same assignee as the present application, it is also known to use the stand-by electric motor as an induction generator while the internal combustion engine is operative, to power fans and defrost heaters. It is an object of the present invention to improve upon the arrangement of the aforesaid patent.